Code-Memo

Kubernetes Networking

Pod networking model

• Each Pod gets its own IP address in the cluster network.
• Pod-to-pod communication is expected to be direct (no port mapping required between pods).
• Implemented by a CNI plugin (how IPs are assigned/routes programmed depends on CNI).

Services

• A Service provides a stable virtual IP/DNS name over a set of pods (endpoints).
• Types: ClusterIP, NodePort, LoadBalancer; plus headless services for direct discovery.

Ingress controllers

• Ingress defines HTTP(S) routing into the cluster (host/path rules).
• An Ingress controller implements it (often L7 proxy) and may handle TLS termination.

CNI plugins concept

• CNI is the interface Kubernetes uses to configure networking for pods.
• CNIs decide: IPAM, routing, encapsulation (VXLAN/Geneve), policies, and integration with cloud networks.

DNS inside Kubernetes

• Cluster DNS resolves service and pod names (e.g., svc.namespace.svc.cluster.local).
• Many app “can’t connect” issues are actually DNS misconfig, search path, or stub resolver behavior.